Contaminant of the Month: Lead

What is it:

Lead is a naturally occurring malleable, dense, blue-gray metal. Its Atomic Number (number of protons in the nucleus) is 82 and its Atomic Weight (average number of protons plus neutrons) is 207.19.
Lead has many commercial uses including its use in lead acid batteries, ceramic glazes, ammunition, leaded glass and solders for electrical equipment. Formerly it was widely used in leaded red and white paint, canned-food container solders, auto radiator solders, production of tetraethyl lead gasoline additive and in drinking water pipe solders.
The chemical symbol for lead is Pb from the Latin plumbum, from which the word plumber was derived. At one time it was used in water pipes because of its ease of manufacture and long-term stability.

Occurrence:

There are four stable isotopes of lead that result from decay of radioactive uranium and thorium. It is possible to determine the geological age of rocks from the composition of the various radionuclides in the decay series and lead.
Lead is widely distributed and occurs as both the metal and many lead salts; for example, lead carbonate and numerous oxides. The principal oxidation states are +2 (PbO) and + 4 (PbO₂). Galena is a common lead sulfide ore.
Organically bound lead (i.e., tetraethyl lead) at one time was widely used as an octane booster gasoline additive. Most leaded paint use has been banned in the U.S. since 1978, but road paints may still contain it. Houses built before 1978 can have lead paint indoors or outdoors.

Health concerns:

Lead is a toxic heavy metal with a half-life in blood of about 30 days. What is not excreted is ultimately deposited in bone, where it can remobilized during pregnancy or aging, or due to calcium dietary deficiency.
The principal environmental exposure risk concern is neurotoxicity especially in infants and young children. Consumption of lead paint, often due to pica, is a high-dose route of exposure and a major lead toxicity concern.
Lead poisoning requiring chelation therapy is identified at 45 µg/dl (µg per 100 cc of blood =µg/dl). Developmental mental deficits can occur at considerably lower concentrations.
Lead blood levels in U.S. children have declined significantly, primarily from the elimination of leaded gasoline and lead can and water pipe solders. Between 1976 and 1980, lead blood levels in children in the U.S. were micrograms per deciliter; they had declined to 2.7 µg/dl by 1991, and 1.9 µg/dl by 2002. Currently, the mean is close to 1 µg/dl. The reference level for children of one to five years of age is now 5 µg/dl, in which case follow-up action is recommended to determine the cause. About 2.5 percent of one- to five-year-olds currently exceed 5 µg/dl. Subtle, but reversible IQ losses are suspected to occur at levels about 5-10 µg/dl.
If not properly managed, renovations of older houses can cause significant blood lead increases in resident children through dust inhalation and pica (ingesting dust and dirt particles).

Water issues and treatment:

The principal sources of exposure from drinking water are leaded brass faucets, old lead service lines and old leaded pipe joint solders. Old galvanized water pipe has been shown to accumulate lead, probably on iron oxide particulates, and significant lead water levels are reached when they are mobilized.
Lead can be leached into drinking water by dissolution, but lead particulates may also be released.
Corrective actions often involve pH or alkalinity adjustments and they might use orthophosphates or silicates to reduce the corrosiveness of the water. If that is insufficient, replacement of lead service lines is required.
There is a debate on the long-term consequences of partial service line replacement; for example, when the public segment from the meter to the water main is replaced, but not the private segment from the home to the water main.
Increased lead extraction has sometimes occurred when water suppliers switched from free chlorine residuals to chloramine residuals. Orthophosphates added at a few mg/l have been successful in restoring the passivized surface on leaded materials, including lead service pipes, and reducing the lead releases.
POU treatments are readily available for lead reduction at the tap, as are pour-through containers. Numerous manufactured products that claim lead reduction are available. They often utilize zeolites as part of the system for removal of dissolved lead. RO and cation exchange are also effective. More recent certifications also require demonstrated lead particulate removal.

Analyses:

Standard methods including ICP/MS and Atomic Absorption are commonly-used analytical procedures for lead. U.S. Environmental Protection Agency (EPA) methods include 200.5, 200.7 and 200.9.
Field analyses for lead in soil, dust and paint use X-ray fluorescence instruments with detections in the ppm range.

Regulations:

Brass with lead content greater than eight percent and lead solder with greater than 0.2 percent lead content were banned from drinking water applications in 1986 by Congress. Lower lead content is now required.
Prior to that time the usual pipe solder contained 50 percent lead and 50 percent tin. Replacement solders are now commonly 95 percent tin and five percent antimony, or 95 percent tin and five percent silver.
The former drinking water Maximum Contaminant Level (MCL) was 50 µg/l collected in running tap water.
The U.S. EPA Lead and Copper rule requires tap monitoring for lead and copper and corrective actions if the action levels were exceeded.
The "action level" for lead is 15 µg/l (not a health-based MCL) in more than 10 percent of the sampled locations in the water supply. It applies to the first liter of water drawn from a faucet where the water has been stagnant for at least six hours or overnight. Its intent was to identify water supplies where the water was excessively corrosive, resulting in lead leaching above the action level.
If the action level is exceeded corrective actions are required to reduce the corrosiveness of the water. This involves pH or alkalinity adjustments and often use of orthophosphates or silicates. If water conditioning treatments are not sufficient then the system will be required to replace any lead service lines.
Reductions of permissible lead in water contact surfaces to 0.25 percent will go into effect in January 2014.

Information Sources: Lead and Copper Rule 56 FR 26460, June 7, 1991. Blood Lead, MMWR, CDC, Vol. 6/No. RR-8, November 2, 2007. Env. Health Perspect. 115(2), 221-225, Feb. 2007. Lead and Copper Rule, http://water.epa.gov/lawsregs/sdwa/index.cfm.

Dr. Cotruvo is president of Joseph Cotruvo and Associates, LLC, Water, Environment and Public Health Consultants. He is a former director of the U.S. EPA Drinking Water Standards Division.